The disclosed embodiments concern a unit comprised of a glidepath aerial and support member for it; the unit is designed to be mounted on the front landing gear of an aircraft, particularly a civilian transport airplane.
Devices are known that help steer an aircraft, particularly the ILS “instrument landing system” to guide an aircraft in its landing phase. This precise instrument runway approach system is particularly useful to the pilot in the event of poor visibility (snowfall, heavy rain . . . ) or in the absence of visibility (thick fog).
Devices are known that help steer an aircraft, particularly the ILS “instrument landing system” to guide an aircraft in its landing phase. This precise instrument runway approach system is particularly useful to the pilot in the event of poor visibility (snowfall, heavy rain . . . ) or in the absence of visibility (thick fog).
When an airplane deviates from its final approach trajectory, this system gives the pilot the lateral deviation compared to the longitudinal axis of the runway and the vertical deviation compared to the glide path for a specific angle of approach. The aircraft can then correct this final approach.
Such a landing system includes, on one hand, automatic stations located on the edge of the landing strip and onboard the airplane, and, on the other hand, a locator and a glidepath aerial. This dual aerial system is generally mounted in the space delimited by the radome in the nose of the airplane. These aerials are then supported by the watertight bulkhead of the fuselage.
This installation principle for the glidepath aerial in the radome follows the operational rules of the International Civil Aviation Organization, mainly for medium-sized airplanes, type WB, SA, LR such as A 330/340 airplanes.
These rules specifically require that the vertical distance to the runway threshold between the trajectory of the bottom of the wheels of the main landing gear and the trajectory of the glidepath be limited to a maximum of 19 feet. This is called the “19-foot rule.”
However, it has been found that airplanes with a longer fuselage than the A380 needed to add a second glidepath aerial called a “GLIDE TRACK” aerial that must be installed in the front of the plane so that it rises on the glidepath when it goes to a predetermined altitude threshold.
The instrument landing system does the switching between these two glidepath aerials.
The requirements in terms of performance of the instrument landing system, classified critical since they are linked to the automatic landing system, condition the installation of this second “GLIDE TRACK” aerial in the front of the plane below the capture aerial.
This positioning makes it possible to prevent the problems of shadows on the charts for the aerial and lever arms in relation to the pilot's eye.
Consequently, it is known how to install this second aerial on the leg of the front landing gear of the airplane.
However, this glidepath aerial is not protected very much or not at all while it is exposed to a particularly hostile environment in the front landing gear area.
First of all, this area is highly exposed during ground maintenance operations because of the presence of the electrical ground connection and the access to the tow bar. Although this work can be done by qualified operators, human error can result in damage to the glidepath aerial.
This area is also vulnerable in flight because of the absence of a ground plane, or radioelectric counterweight, stable from an electrical standpoint. Indeed, the equipotential of this ground plane with the nose cone of the fuselage is difficult to control, considering the joints and rotating bearings used at the junction of the front landing gear/nose cone.
Moreover, the different elements of which the front landing gear is composed generate a very wide vibratory spectrum that can interfere with the aerial function.
What is more, it is necessary to take into account the aerodynamic effect of the leg/wheel unit on the physical maintenance of the beams connecting this aerial to the receiver in the airplane fuselage, mainly at the interface between the jointed front landing gear/gear housing. It is also necessary to take into account the promiscuity of the electrical and hydraulic circuits along the leg of the landing gear, which can cause serious malfunctions if leaks appear in the hydraulic circuits.
Lastly, this glidepath aerial is particularly exposed to severe meteorological conditions that can occur in flight, such as hail and lightning.
All these elements interfere with the proper operation of this second glidepath aerial by generating interference that is superimposed on the “Glide” deviation (DDM modulation difference) generated by the receiving unit of the MMR-type (multi-mode receiver) auxiliary landing receiver.